NATO's commander in Afghanistan said Thursday that efforts to drive the Taliban out of the country's Kandahar region are going slower than expected. The remarks were made on the sidelines of a key NATO meeting in Brussels.

U.S. Army General Stanley McChrystal acknowledged that efforts to route out the Taliban insurgency in the Kandahar were going slower than the alliance originally anticipated.

"It is my personal assessment that it will be more deliberate than we probably communicated or than we thought earlier and probably communicated," McChrystal said. "So I think it will take a number of months for this to play out. But I don't necessarily think it's a bad thing. I think it's more important that we get it right than we get it fast."

McChrystal spoke to reporters at the start of a two-day NATO defense ministers meeting that is expected to focus on Afghanistan, among other topics. About 20 NATO troops have been killed in militant attacks in Afghanistan since Monday.

Public frustration is also growing in Europe and the United States after nearly nine years of fighting the Taliban.

Speaking in London earlier this week, U.S. Defense Secretary Robert Gates said Washington is considering sending reinforcements to help British troops fighting in Afghanistan's Helmand province, which borders Kandahar.

McChrystal said he expects the violence to continue in the near-term.

"There are going to be tough days ahead," McChrystal said. "Violence is up and I think that violence will continue to rise, particularly over the summer months. It's necessary [that] we roll back Taliban influence as we move toward increased security in the future."

NATO's Secretary General Anders Fogh Rasmussen is urging alliance members to make good on pledges to send trainers to Afghanistan to boost the numbers of Afghan military and police.